1. Field of the Invention
The invention relates to a smoothing device for flat printing materials. A leading edge of a printing material is pulled over guide surface sections which form a smoothing notch and have at least one air passage opening which communicates with a flow duct. During operation, the at least one air passage opening provides pressure conditions which form a bead in the printing material that projects into the smoothing notch. The invention also relates to a printing machine equipped with the smoothing device.
A smoothing device of the type described above is disclosed, for example, in German Patent No. DE 26 49 051 C2. During proper use of this smoothing device, its flow duct is connected to a vacuum generator which sucks a section of the printing material, which is momentarily located in the region of the smoothing notch, into the smoothing notch, forming a bead in the printing material. In this case, the guide surface sections, which are generally placed in a direction of travel upstream and downstream from the smoothing notch, and to a great extent also the guide surface sections forming the smoothing notch are in contact with the printing material which is drawn over them, this contact being particularly intimate in the region of the smoothing notch, because of the forces acting there on the printing material in the direction of the corresponding guide surface sections, and these forces giving rise to considerable frictional forces on the printing material, which can lead to marks being produced on the printing material.
It is accordingly an object of the invention to provide a smoothing device which overcomes the above-mentioned disadvantages of the heretofore-known smoothing devices of this general type and which can be used to smooth printing materials carefully and gently.
With the foregoing and other objects in view there is provided, in accordance with the invention, a smoothing device, including:
guide surface sections for a flat printing material having a leading edge being pulled with positive guidance in a direction of travel over the guide surface sections;
throttling ducts pressurized with compressed air during operation;
the guide surface sections having openings formed therein, the openings communicating with the throttling ducts;
a flow duct; and
the guide surface sections forming a smoothing notch and having at least one air passage opening formed therein, the at least one air passage opening communicating with the flow duct, and the at least one air passage opening being configured to cause pressure conditions when there is an air throughflow during operation such that the flat printing material forms a bead projecting into the smoothing notch.
In other words, according to the invention, a smoothing device for flat printing materials which, with positive guidance of a printing material edge that leads in the running direction, are pulled over guide surface sections which form a smoothing notch and have at least one air passage opening which communicates with a flow duct and which, when there is throughflow during operation, gives rise to pressure conditions which, in the printing material, form a bead projecting into the smoothing notch, wherein the guide surface sections are provided with openings which communicate with throttling ducts, and wherein during operation the throttling ducts have compressed air applied to them.
A smoothing device configured in such a way develops, in addition to the suction action forming the aforementioned bead on the printing material, a supporting action which prevents any contact between the printing material and the guide surface sections which are provided with the openings communicating with the throttling ducts. This supporting action results in a manner which is advantageous insofar as it is developed at low volume flow and thus does not excite any fluttering of the printing material. Moreover, the supporting action is improved, i.e. increased, as the printing material approaches more closely to the guide surface sections provided with the openings, because of the volume flow of the throttled flow, which decreases in the process, so that between these guide surface sections and the printing material pulled over them, a pressure builds up which corresponds approximately to that at which the compressed air is fed into the throttling ducts.
According to another feature of the invention, the throttling ducts are formed by lamellae, two of the lamellae are spaced from one another by a given distance and are provided opposite one another, the two of the lamellae form contiguous flow duct sections therebetween, and the contiguous flow duct sections have a repeatedly changing flow direction.
According to a further feature of the invention, the throttling ducts are formed by at least one channel communicating with at least one inlet opening and at least one outlet opening and by a filter acting between the at least one inlet opening and the at least one outlet opening.
According to another feature of the invention, the filter is formed by a textile insert, an air-permeable bulk material filling, fibers, an air-permeable structure formed from a sintered material or an insert having an air-permeable sponge structure.
According to yet another feature of the invention, the throttling ducts are embodied by a cushion filled with platelets and having an air-permeable cushion cover.
According to a further feature of the invention, a chamber having a compressed-air connection is provided, the chamber forms one of the guide surface sections, and the throttling ducts are formed by a throttling insert adjoining the openings, and the throttling insert acts between the openings and the compressed-air connection.
According to a further feature of the invention, the throttling insert includes an air-permeable bulk material filling, a textile material, fibers, an air-permeable structure formed from a sintered material or an air-permeable sponge structure.
According to another feature of the invention, the throttling ducts are formed by a dimensionally stable throttling insert, the dimensionally stable throttling insert forms one of the surface guide sections with the openings formed therein.
According to another feature of the invention, the at least one air passage opening includes a plurality of air passage openings provided along the smoothing notch, the smoothing notch having an extent substantially transverse to the direction of travel, the air passage openings form a central group and edge groups with respect to the extent of the smoothing notch, and the central group communicates directly with the flow duct, and the edge groups communicate indirectly with the flow duct via the throttling ducts.
According to a further feature of the invention, the throttling ducts associated with the edge groups are formed by lamellae, two of the lamellae are spaced from one another by a given distance and are provided opposite one another, the two of the lamellae form contiguous flow duct sections therebetween, and the contiguous flow duct sections have a repeatedly changing flow direction.
According to a further feature of the invention, the throttling ducts associated with the edge groups are formed by at least one channel communicating with at least one inlet opening and at least one outlet opening and by a filter acting between the at least one inlet opening and the at least one outlet opening.
According to yet a further feature of the invention, the throttling ducts associated with the edge groups are formed by textile inserts or an air-permeable bulk material filling.
According to another feature of the invention, the filter includes fibers, an air-permeable structure formed from a sintered material or an insert having an air-permeable sponge structure.
According to a further feature of the invention, the throttling ducts associated with the edge groups are embodied by a cushion filled with platelets and having an air-permeable cushion cover.
According to yet a further feature of the invention, the throttling ducts are formed by throttling inserts, the air passage openings of the edge groups communicate with the flow duct via the throttling inserts.
According to another feature of the invention, the throttling inserts associated with the edge groups include an air-permeable bulk material filling, a textile material, fibers, an air-permeable structure formed from a sintered material or an air-permeable sponge structure.
According to a further feature of the invention, the throttling inserts associated with the edge groups are dimensionally stable throttling inserts.
According to another feature of the invention, further guide surface sections are provided upstream from the smoothing notch with respect to the direction of travel; the further guide surface sections form a further smoothing notch and have further air passage openings formed therein; the further air passage openings are configured to cause pressure conditions when there is an air throughflow during operation such that the flat printing material forms a further bead projecting into the further smoothing notch; further throttling ducts, which are pressurized with compressed air during operation, are provided; and a further flow duct is provided, the further air passage openings communicate with the further flow duct via the further throttling ducts.
According to a further feature of the invention, the further throttling ducts associated with the further air passage openings are formed by lamellae, two of the lamellae are spaced from one another by a given distance and are provided opposite one another, the two of the lamellae form contiguous flow duct sections therebetween, and the contiguous flow duct sections have a repeatedly changing flow direction.
According to yet a further feature of the invention, the further throttling ducts associated with the further air passage openings are formed by at least one channel communicating with at least one inlet opening and at least one outlet opening and by a filter acting between the at least one inlet opening and the at least one outlet opening.
According to another feature of the invention, the further throttling ducts associated with the further air passage openings are formed by a structure selected from the group consisting of a textile insert, an air-permeable bulk material filling, fibers, an air-permeable structure formed from a sintered material, an insert having an air-permeable sponge structure, and a cushion filled with platelets and having an air-permeable cushion cover.
According to another feature of the invention, a suction air connection is provided on the further flow duct; and the further throttling ducts are formed by a throttling insert acting between the further air passage openings and the suction air connection.
According to a further feature of the invention, the throttling insert includes an element selected from the group consisting of an air-permeable bulk material filling, a textile material, fibers, an air-permeable structure formed from a sintered material, and an air-permeable sponge structure.
According to a further feature of the invention, the throttling insert is a dimensionally stable throttling insert.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a smoothing device for flat printing materials, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.